More than 150 governments gathered in this traditional stronghold of the Sicilian Mafia yesterday, to sign a treaty bringing international law enforcement into the high-tech, high speed, globalized new century.

The United Nations Convention Against Transnational Organized Crime - the first such international treaty - is a bid to help national police forces work as smoothly and efficiently together as do their targets. It will bolster existing international crime busters - like Interpol and the FBI - by enacting laws that support their efforts. Outlawing bank secrecy, keeping prosecutors worldwide in e-mail contact, and setting up international witness protection programs are among the treaty's goals.

Harmonizing laws and ways of implementing them, the convention "means we will go from the speed of an automobile to the speed of an aircraft" in mob-busting operations, says Pino Arlacchi, head of the UN Office for Drug Control and Crime Prevention. "This is a state-of-the-art instrument in the fight against organized crime."

Open borders and modern communications technologies have done more than ease legal travel and trade. They have also enabled criminals to set up networks that span the globe.

Where once mobsters moved bootleg liquor from Canada into the United States, today Chinese "snakehead" gangs can smuggle illegal immigrants from Shanghai to Western Europe and America, and Colombian cocaine producers are hooked into planetwide distribution networks.

The new convention makes law enforcement equally global. For the first time, boasts Professor Arlacchi, "We have a universal standard to fight the Mafia."

Organized criminal gangs "have wasted no time" in adapting new technologies to their ends, said UN Secretary-General Kofi Annan, who opened the four-day conference. "But our efforts to combat them have remained until now very fragmented and our weapons almost obsolete." The convention, he added, would encourage people to recognize that mafias "are not invincible" - a lesson that Palermo has taught in a fierce and unexpectedly successful battle against the "Cosa Nostra" in recent years.

The treaty sets out an agreed definition of just what serious organized crime is. In the past, lack of such a definition has proved an often insuperable obstacle to investigators from different countries trying to help each other. When national parliaments have amended their laws to match the treaty, cooperation will be easier and quicker, UN officials say.

Prosecutors are often stymied as they follow international trails of suspects, when they find that what is a crime in their country is not illegal where their quarry is living. Italian police, for example, know that hundreds of Italian mafiosi are living peacefully in Caribbean islands where membership in a criminal organization is not illegal. That makes prosecution and extradition impossible. Under the convention, membership in an organized crime group will be a criminal offense. So will money laundering, which is not against the law in many countries, including Russia. Corruption and obstruction of justice will also be made international criminal acts.

Taking aim at smugglers of drugs, people, and arms, who make up the bulk of international organized criminals, the treaty brings to bear weapons found in some national armories already, such as the confiscation of criminal assets, witness-protection programs, and the abolition of bank secrecy.

The convention also brings international judicial cooperation into the 21st century, providing for international arrest warrants to be sent by e-mail, rather than time-consuming diplomatic channels, and for videoconferences that would allow witnesses to testify without having to travel halfway around the world.

A number of financial centers whose bank secrecy makes them tax havens, among them the tiny European principality of Lichtenstein, have agreed to sign the convention, UN officials say. Though their practices are not in line with the convention's language - which obliges governments to cooperate with international requests for assets to be identified or frozen - their presence "is a demonstration of their willingness to start a process," Arlacchi says.

Countries that rooted hard for a strong treaty say they are happy with the results, which, once ratified by 40 nations, will have the force of international law. "The convention and its two protocols [on the trafficking of drugs and on trafficking in humans, especially women and children] live up to almost all the hopes we had of them," says Frank Loy, undersecretary of State for global affairs, who headed the US delegation.

Though some developing countries worried about the costs of implementing the treaty, their fears were assuaged by a clause that provides for a special fund, made up of assets seized from mobsters, that will help pay for the extra work they will have to do to live up to the convention.

Those funds could be substantial. The International Monetary Fund has estimated that the illegal economy adds up to between 3 percent and 5 percent of the global gross national product.

But Arlacchi sees even greater benefits from the convention, if enough countries ratify it and bring their laws into line.

"This is not just a question of mafias," he says. "It is macropolitics. Whole countries have been destabilized by organized crime, from Russia to Albania to Sierra Leone. This convention is a way they can protect themselves from a new source of instability."